Regarding html and DOCTYPE and conditional statement

Basically what will happen is that you'll get your page rendered in a "standards mode".

The only reason why you probably shouldn't use the new DOCTYPE is if you want to use XHTML 1.0 markup and conform to XHTML 1.0.

The downside to using HTML5 now is that the spec can change. This makes it important for you to keep up with the spec as it actively changes.

With that being said, I've already started using the new syntax in my pages. Also it guarantees that your page will last for a very, very, long time.

So go ahead, use it (and learn to love how simple it is).

Go through this links it will help you

https://css-tricks.com/how-to-create-an-ie-only-stylesheet/

http://stackoverflow.com/questions/18787602/if-lt-ie-7-html-class-ie-ie6-lang-en-endif